What ya gonna do? You gonna use gonna? Wouldja use woulda, shoulda, coulda? It’s a heckuva choice and a helluva situation for a copy editor.
We all know that spoken language differs substantially from written language, and putting the former into the latter is fraught with difficulties. Written language supplies capitalization, punctuation, spelling while omitting, for the most part, nonverbal noises. But what is written should coincide in some substantial way with what was spoken.
Moreover, as we strive to make what is written more conversational than formal, at least in journalism, writers increasingly want the text to sound like speech to the reader’s mind. Hence the phonetic spellings above. People do talk like that, after all.
The question for editors is how far to go, in the translation, or rather transliteration, of spoken English into some form of the standard written dialect. In his later published work, J.D. Salinger took to italicizing syllables of words to indicate the speaker’s emphasis. Were we to reproduce spoken language thus, in a misguided attempt to represent the rhythms of speech, it would drive you nuts.
There is also the hazard, addressed in the post "You can quote me" from April 3 of this year, that phonetic representation of speech can look like condescension to the speaker, or even ridicule.
So we coulda used helluva, but we decided not to, and we aren’t gonna. You wanna make something of it? That’s what the comment function is for.